1. Field of the Invention
The present invention relates to an acrylic rubber composition that is unlikely to deteriorate even when it is exposed to high temperature for a long time and that has excellent heat resistance and a cross-linked product of the composition.
2. Description of the Related Art
An acrylic rubber composition has excellent heat resistance and oil resistance and hence has been used for hoses and seals in the engine compartment of automobiles. However, due to recent emission controls, higher engine power, and the like, such a member has been used in a much higher temperature condition, and thus the component is required to have higher heat resistance than ever before.
An unvulcanized acrylic rubber is likely to adhere to a metal surface of a kneading machine such as a Banbury mixer, a kneader, and an open-roll kneader during kneading and thus such a kneading machine often requires cleaning after the kneading. On this account, there is a demand for an acrylic rubber that is unlikely to adhere to the metal surface and has excellent processability.
There are a known acrylic rubber composition including a cross-linking site having a carboxyl group as an acrylic rubber material having processability, mechanical characteristics, compression set characteristics, heat resistance, and the like in balance (for example, see Patent Document 1) and a known technique of mixing a particular carbon black to an acrylic rubber composition.
As an approach to improve the heat resistance of the acrylic rubber, there is a technique of blending an extreme elastomer (an elastomer having excellent heat resistance and oil resistance, such as a fluorocarbon rubber, a fluorosilicone rubber, and a silicone rubber) to the acrylic rubber. Known examples include a technique of blending a silicone rubber to an acrylic rubber for peroxide cross-linking (for example, see Non-Patent Document 1).
For the prevention of the adhesion to a metal surface, the addition of an internal mold release agent such as an ester wax, a paraffin wax, and a silicone oil to the acrylic rubber is considered to be effective. For example, for the improvement of roll adhesiveness, there is disclosed a technique of adding a silicone oil having a methacryl group in the molecule to an acrylic rubber (Patent Document 3). However, there is no description about a carboxy group-containing acrylic rubber and about the effect on heat resistance in Patent Document 3. The carboxy group-containing acrylic rubber has excellent heat resistance while it has poor roll adhesiveness and therefore there is a demand for a method for solving such a problem.
There is also known acrylic rubber composition including an unsaturated dicarboxylic acid monoalkyl ester copolymerized acrylic elastomer and an amine vulcanizing agent in order to improve oil resistance, compression set characteristics, and the like (Patent Document 4). However, the acrylic rubber composition produces a vulcanized product having insufficient heat resistance and is required to be improved.